Existing motion-capture systems may detect infrared (IR) signals with expensive digital cameras having one or more lenses. The IR signals may be emitted from active markers or a ring of LEDs surrounding each lens which cause light to be bounced off of retro-reflective passive markers affixed to the object being tracked. These motion-capture systems may require at least three cameras to be effective. Some systems operate with more than six cameras, and some systems are scaled up to even 300 cameras.
However, currently available motion-capture systems may only record three-dimensional (3D) positions of single points, describing an object's motion in left-to-right, up-and-down or forward-and-backward. Data with six degrees of freedom (6DoF), including rotational movement about the x-, y- and z-axes, is often highly valuable for body position analysis in medicine, in virtual reality mechanics, and in reality-based animation, among other applications. In order to approximate 6 degrees of freedom, a motion-capture technician may currently need to apply and track three or more passive markers to get a single 6DoF description.
Problems can occur with camera-based motion capture when the three markers are close together physically or have apparent angles, relative to individual cameras, that are very nearly the same. Further issues can arise if the cluster of markers is too far or too close to any of the cameras. Messy merging of these passive markers often results, which contaminates and degrades 6DoF matrix data output. After recording data, each passive marker must be individually labeled, and picked-up again if momentarily dropped. Additionally, even when working with very accurate motion-capture data, animations produced from the captured data often get trapped in the “uncanny valley” where realism is not truly felt and audiences may react negatively. Part of today's failure to create realism occurs because the passive markers used to capture an actor's face may only yield 3DoF data. For example, it may be physically impossible to provide enough adjacent markers to track features such as the curl of the lip in 6DoF. There are hybridized motion-capture systems that pair passive markers with inertial sensors, but such systems may have increased complexity and suffer from so-called “double differential” errors.